Anticoagulation therapy — choice, initiation and reversal viva

Opening scenario

The examiner presents a patient on warfarin (mechanical mitral valve, INR target 2.5-3.5) who presents with a life-threatening gastrointestinal bleed, and asks: "What is your immediate management, and how would you reverse the anticoagulation?"

Interpretation

• Diagnosis: major anticoagulant-related bleed on warfarin (the mechanical mitral valve is the indication; the GI bleed is life-threatening).
• The critical action is immediate reversal while resuscitating — do NOT delay for further investigations.^[1]

Key points the examiner will probe

Be ready to defend each of these at viva depth:

1. Classification of anticoagulants — parenteral heparins (UFH, LMWH, fondaparinux) which require antithrombin as cofactor; warfarin which inhibits VKORC1 (hepatic vitamin K cycle, factors II/VII/IX/X + protein C/S); DOACs which act directly — dabigatran on IIa, rivaroxaban/apixaban/edoxaban on Xa. Each drug's site of action predicts its onset, monitoring, and reversal.^[1]

2. Warfarin mechanism in detail — warfarin inhibits VKORC1, blocking the recycling of vitamin K epoxide to active reduced vitamin K; gamma-glutamyl carboxylase cannot carboxylate factors II, VII, IX, X and proteins C/S → these are synthesised but functionally inactive (PIVKA proteins). Onset is 3-5 days because factor II half-life is 60-72 h. Bridge with LMWH. CYP2C9 and VKORC1 polymorphisms explain dose variability.^[1]

3. Reversal ladder for warfarin — life-threatening bleed (ICH, retroperitoneal): STOP warfarin, vitamin K 10 mg IV slow + four-factor PCC 25-50 IU/kg (faster and smaller volume than FFP); always give PCC WITH vitamin K (PCC factors decay 6-8 h; vitamin K synthesises new ones). INR 5-9 no bleed: hold, oral vitamin K 1-2.5 mg. INR over 9 no bleed: hold, oral vitamin K 2.5-5 mg. Avoid IV vitamin K for non-life-threatening situations (anaphylactoid reaction; causes warfarin resistance for 7-14 days).^[1]

4. DOAC reversal — dabigatran: idarucizumab 5 g IV (humanised monoclonal Fab, RE-VERSE AD). Apixaban/rivaroxaban/edoxaban: andexanet alfa (modified Xa decoy, ANNEXA-4) or PCC 50 IU/kg if unavailable. Dabigatran can be dialysed (50-60 percent removed); Xa inhibitors cannot (highly protein-bound).^[1]

5. DOAC vs warfarin by indication — DOAC first-line for non-valvular AF (NICE NG196), unprovoked VTE, cancer-VTE (apixaban/rivaroxaban); warfarin MANDATORY for mechanical valve (RE-ALIGN — dabigatran had more thrombosis AND more bleeding), triple-positive antiphospholipid syndrome (TRAPS), rheumatic mitral stenosis with AF; LMWH in pregnancy (warfarin teratogenic weeks 6-12; DOACs contraindicated).^[5][8]

6. Risk stratification — CHA2DS2-VASc (stroke risk: C HF, H HTN, A 75+ [2], D diabetes, S stroke/TIA [2], V vascular, A 65-74, Sc female); anticoagulate at score 2+ (men) or 3+ (women). HAS-BLED (bleed risk: H HTN SBP over 160, A abnormal renal/liver [max 2], S stroke, B bleeding, L labile INR, E elderly, D drugs/alcohol); score 3+ = high bleed risk — does NOT contraindicate anticoagulation, prompts modification of reversible factors (BP, NSAIDs, alcohol).^[8]

7. Initiation specifics — warfarin loading 5 mg (10 mg young/fit); bridge with LMWH (1.5 mg/kg OD treatment, 40 mg OD prophylaxis) until INR in range 2 consecutive days. Apixaban AF: 5 mg BD (2.5 mg BD if 2 of 3 — age 80+, weight 60 kg or less, creatinine 133+). Rivaroxaban VTE: 15 mg BD for 3 weeks then 20 mg OD (with food). Dabigatran AF: 150 mg BD (110 mg if age 80+ or eGFR 30-50). All DOACs renal-dose-adjust.^[1]

8. Complications — HIT (IgG to heparin-PF4; platelets drop 50 percent or below 150 within 5-14 days; stop ALL heparin; argatroban in renal failure); warfarin skin necrosis (protein C deficiency; 3-10 days; breast/buttock/thigh); heparin-induced osteoporosis (UFH over 1 month).

9. Peri-operative management — warfarin stop 5 days (bridge if high-risk: mechanical mitral, recent VTE/stroke under 3 mo); DOAC stop 24-48 h (no bridge); restart once haemostasis secure (warfarin day 1-2, DOAC 24 h low-bleed risk, 48-72 h high-bleed).

10. Pitfalls — not bridging warfarin in high-risk indications; bridging DOACs (unnecessary); forgetting renal dose adjustment in acute illness; misreading a normal INR as "DOAC safe" (INR is insensitive to DOACs).

References

1. Harter K, et al. Anticoagulation drug therapy: a review. West J Emerg Med 2015.^[1]
2. Eikelboom JW, et al. RE-ALIGN: dabigatran in mechanical heart valves. N Engl J Med 2013.^[5]
3. NICE NG196: Atrial fibrillation. 2021.^[8]

References3ShowHide

1. [1]Harter K, Levine M, Henderson SO. Anticoagulation drug therapy: a review. West J Emerg Med, 2015.PMID 25671002
2. [5]Eikelboom JW, et al. Dabigatran vs warfarin in mechanical heart valves (RE-ALIGN). N Engl J Med, 2013.PMID 23991661
3. [8]NICE. Atrial fibrillation: diagnosis and management (NG196). NICE, 2021.Source